A recent poll suggests that a unnamed Tea Party candidate would beat an unnamed Republican candidate for president if election was held now. The most important message in that poll was more people chose the Tea Party and GOP combined than did the Democrat, however, in a three way unnamed race the Tea Party and GOP split the votes giving the Democrat the win.
This is exactly the dynamics that a third party candidate gives to a presidential race, and for that matter a Congressional and Senate race. It splits those who most agree and gives the candidate that the least voters agree with the win.
The most recent examples were the 1992 election where the wild card of Ross Perot, the populist independent candidate who would have been the darling of the Tea Partiers. It ended with Clinton getting 43.01% of the vote, George H.W.Bush with 37.45%, and Ross Perot with 18.91%. Those who voted for Perot would have overwhelmingly gone Bush if Perot wouldn't have been in the race. Clinton won reelection with less only 49% as Perot still carried a little over 8% in 1996 as well.
The end result of a third party candidate can be dire to America. In 2012 it would mean another term for Obama and his regime. Back in 1840 a third party candidate may well have caused the Civil War.
James Gillespie Birney, a slaveholder from Kentucky, who converted to abolitionism. He, like many religious converts, became a zealot for his cause. He gave up a lucrative law practice in Alabama to become an agent of the American Colonization Society, which supported political actions to end slavery and resettle freed slaves in Africa and the Caribbean. After he freed his inherited slaves, Birney began to publish an abolitionist newspaper, the Philanthropist, in Cincinnati and became executive director of Garrison's American Anti-Slavery Society. In the presidential elections of 1840 and 1844 he was the candidate for the Liberty Party, which advocated the abolition of slavery by moral persuasion and political action.
His third party candidacy in 1844 was particularly significant, because he drew enough popular votes to allow the Democrat candidate, James K. Polk, to win the election, defeating the Whig candidate, Henry Clay. An adroit politician and master of the art of compromise, he was known as "The Great Compromiser." Clay was a slaveholder who was dedicated to the Union and looked for an end of slavery. Ironically, he might have been the strong president who could have found a political solution to end slavery, and ending the very thing that caused the Civil War seventeen years later.
Third parties may have good people in them, they may have great intentions, but they never win, and often cause great loss to America.